1. Field of Invention
The present invention relates to an ophthalmoscopic camera, and more particularly to an ophthalmoscopic camera having focus detecting means. More specifically, the present invention pertains to an ophthalmoscopic camera having focus detecting means including mark projecting means for projecting a mark to a patient's eye for detecting focus conditions of the camera.
2. Description of Prior Art
Hithertofore, there has been proposed for the purpose of facilitating focus adjustments to provide an ophthalmoscopic camera with a focus detecting system. An example of such focus detecting system includes a mark projecting optical system having a mark plate located in conjugate with the image plane of the photographing optical system with respect to the objective lens of the camera and a split-prism device for dividing a beam of light from the mark plate into a pair of beams emitting in different angles. The pair of beams are passed respectively through a pair of apertures located in conjugate with the pupil of the patient's eye so that the beams form images of the apertures at the pupil of the patient's eye and an image of the mark at the eye fundus. Thus, an operator can know the focusing condition of the camera on the eye fundus by the image of the mark. In order to make it easy to judge the focus condition by the mark image, it is desirable to make the distance between the aperture images at the pupil as large as possible within the confine of the pupil.
It should however be noted that the ophthalmoscopic camera is used not only with its optical axis in alignment with the optical axis of the patient's eye but also with its optical axis inclined with respect to the optical axis of the patient's eye so as to take pictures of peripheral portions of the patient's eye. Where the optical axis of the camera is inclined with respect to the optical axis of the patient's eye, the pupil of the patient's eye has an elliptical configuration as seen in the direction of the optical axis of the camera. Thus, when the two beams of light projected through the pair of apertures are arranged in a direction of minor axis of the ellipse, the beams may be blocked by the patient's eye.